#include "apue.h"#include <stropts.h>#define	BUFFSIZE	4096intmain(void){	int				n, flag;	char			ctlbuf[BUFFSIZE], datbuf[BUFFSIZE];	struct strbuf	ctl, dat;	ctl.buf = ctlbuf;	ctl.maxlen = BUFFSIZE;	dat.buf = datbuf;	dat.maxlen = BUFFSIZE;	for ( ; ; ) {		flag = 0;		/* return any message */		if ((n = getmsg(STDIN_FILENO, &ctl, &dat, &flag)) < 0)			err_sys("getmsg error");		fprintf(stderr, "flag = %d, ctl.len = %d, dat.len = %d\n",		  flag, ctl.len, dat.len);		if (dat.len == 0)			exit(0);		else if (dat.len > 0)			if (write(STDOUT_FILENO, dat.buf, dat.len) != dat.len)				err_sys("write error");	}}